Learning-Bitcoin-from-the-Command-Line/16_6_Using_Other_Functions_in_Libwally.md

16.6: Using Other Functions in Libwally

NOTE: This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.

Libwally is an extensive library that provides a considerable amount of wallet-related functionality, much of it not available through bitcoin-cli. Following is an overview of some functionality not otherwise covered in this chapter.

Using Cryptographic Functions

A number of cryptographic functions can be directly accessed from Libwally:

• wally_aes — Use AES encryption or decryption
• wally_aes_cbc — Use AES encryption or decryption in CBC mode
• wally_hash160 — Use RIPEMD-160(SHA-256) hash
• wally_scrypt — Use Scrypt key derivation
• wally_sha256 — Use SHA256 hash
• wally_sha256_midstate — Use SHA256 to hash only the first chunk of data
• wally_sha256d — Conduct a SHA256 double-hash
• wally_sha512 — Use SHA512 hash

There are also HMAC functions for the two SHA hashes, which are used generate message-authentication-codes based on the hashes. They're used in BIP32, among other places.

• wally_hmac_sha256
• wally_hmac_sha512

Additional functions cover PBKDF2 key derivation and elliptic-curve math.

Using Address Functions

Libwally contains a number of functions that can be used to import, export, and translate Bitcoin addresses.

Some convert back and forth between addresses and scriptPubKey bytes:

• wally_addr_segwit_from_bytes — Convert a witness program (in bytes) into a Segwit address
• wally_addr_segwit_to_bytes — Convert a Segwit address into a scriptPubKey (in bytes)
• wally_address_to_scriptpubkey — Convert a legacy address into a scriptPubKey(in bytes)
• wally_scriptpubkey_to_address — Convert a scriptPubKey (in bytes) into a legacy address

Some relate to the wallet import format (WIF):

• wally_wif_from_bytes — Convert a private key (in bytes) to a WIF
• wally_wif_is_uncompressed — Determines if a WIF is uncompressed
• wally_wif_to_address — Derivate a P2PKH address from a WIF
• wally_wif_to_bytes — Convert a WIF to a private key (in bytes)
• wally_wif_to_public_key — Derive a public key (in bytes) from a WIF

Using BIP32 Functions

There are additional BIP32 HD-wallet functions, beyond what was covered in §16.3: Using BIP32 in Libwally.

• bip32_key_get_fingerprint — Generate a BIP32 fingerprint for an extended key
• bip32_key_serialize — Transform an extended key into serialized bytes
• bip32_key_strip_private_key — Convert an extended private key to an extended public key
• bip32_key_unserialize — Transform serialized bytes into an extended key

There are also numerous various depending on you want to allocate memory of have Libwally doing the _alloc for you.

Using BIP38 Functions

BIP38 allows for the creation of password-protected private key. We do not teach it because we consider inserting this sort of human factor into key management dangerous. See #SmartCustody.

The main functions are:

• bip38_from_private_key — Encode a private key using BIP38
• bip38_to_private_key — Decode a private key using BIP38

Using Elements Function2

Libwally can be compiled to be used with Blockstream's Elements, which includes access to its assets functions.